The thermal fatigue behavior of the combustor alloys In 617 and HAYNES 230 before and after welding
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mmercial superalloys IN* 617 and HAYNES** *IN is a trademark of Inco Alloys International, Inc., Huntington, WV. **HAYNES is a trademark of Haynes International.
230 are primarily solid-solution and carbide-strengthened alloys, based on Ni-Cr-Co-Mo and Ni-Cr-W, respectively. IN 617 was developed by INCO in the years between 1960 and 1970;[1,2] HAYNES 230 was introduced about 10 years later by Haynes International.[3,4] Both alloys have good high-temperature strength and corrosion resistance. Therefore, they have found wide use, particularly in sheet-product form for welded structures, in the hot paths in the gas turbine, e.g., burners, transition liners, and hotgas casings.[5] In addition to excellent oxidation resistance
F. MEYER-OLBERSLEBEN, Materials Engineer, formerly with the Swiss Federal Institute of Technology, is with Siemens AG, Power Generation (KWU), Mu¨lheim, Germany. N. KASIK, Senior Metallurgist, is with ABB Power Generation Ltd., Baden, Switzerland. B. ILSCHNER, Emeritus Professor of Mechanical Metallurgy, is with the Swiss Federal Institute of Technology, Lausanne, Switzerland. F. RE´ZAI¨-ARIA, Research Associate, formerly with the Swiss Federal Institute of Technology, is with Ecole des Mines d’Albi-Carmaux, 81013 Albi Cedex 9, France. (corresponding address, e.mail:[email protected]) Manuscript submitted June 3, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
and creep strength, a high fatigue strength is required for such components. They are often subjected to repeated cyclic deformation caused by mechanical and/or thermally induced stresses during service, but mainly during startups and shutdowns. This is particularly dangerous if hot spots occur on the surface of the combustor parts. Rapid temperature changes, combined with high-temperature gradients inside the gas turbine components, induce thermal fatigue (TF) loading. While low-cycle fatigue (LCF) and high-cycle fatigue data for these alloys at constant temperature have been established earlier,[6,7,8] their resistance to TF has not yet been tested, though it may well be the most important life-limiting factor for cyclically operated gas turbines. Furthermore, it is now well recognized that isothermal LCF data may not be sufficient for the prediction and evaluation of thermal-mechanical fatigue (TMF) life.[9,10] Previous tests on superalloys, which are typically used for blades, have demonstrated that TF can be the most dangerous loading mode, as compared to isothermal LCF and also to TMF within a comparable temperature range.[11,12] Therefore, it was decided to perform TF tests on the alloys IN 617 and HAYNES 230. Within this work, the edges of single-wedge specimens, machined from the two aforementioned alloys have been induction heated and pressurized-air cooled within various temperature ranges and thermal gradients. In this type of VOLUME 30A, APRIL 1999—981
Table I.
Chemical Composition of Alloys Used (Weight Percent)
Alloy
Ni
Cr
W
Mo
Fe
Co
Mn
Si
Al
C
La
B
Ti
IN 617 HAYNES 230
bal bal
22.1 22.2
— 14.2
9.1 1.26
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